It is well known that separate, but sometimes closely spaced, quantities of coolant and lubrication oil are employed in the operation of liquid-cooled, internal combustion piston engines. In the construction of such engines, an engine cylinder block is employed in a closely fitting, sealing relationship with a cylinder head block. Depending upon its configuration of cylinders (e.g., "in line" or "V"), the cylinder block is formed with one or two upper flat deck surfaces against which an overlying cylinder head(s) is bolted. Since both the engine block and head contain oil and coolant passages, a head gasket is interposed between them as a seal to keep the liquids separated as well as seal the cylinder bores.
The engine lubricating oil is a mixture of hydrophobic organic compounds with stabilizing additives, and the coolant is a homogeneous mixture of ethylene or propylene glycol with water and dissolved stabilizing and corrosion-inhibiting additives. The coolant pressure may at times exceed the oil pressure and may leak across the head gasket interfaces into the oil despite the presence of the head gasket.
Proper sealing between the coolant and oiling systems in an engine is of paramount importance to engine durability. Small amounts of coolant contamination in the oil lead to rust and to degradation of oil by removal and decomposition of oil additives. A large amount of coolant contamination can lead to bearing failure due to a loss of bearing load capacity. Significant efforts have been made to design head gaskets that provide durable sealing of the engine cooling system.
Engineers involved in the design or modification of engines need to have a method, other than trial and error, of determining the leakage path of the coolant in order to specify gasket design, bolt location, torque requirements or the like. Techniques that are currently available to measure small rates of coolant leakage are inadequate. Measurement of glycol in oil is only semi-quantitative, and coolant may be lost from the oil by degradation, evaporation or inclusion in engine deposits. Quantitative determination of coolant leakage is possible for coolants that employ potassium salts by measuring the potassium levels in the oil. However, sensitivity is limited because of the relatively small amount of potassium in the coolant. Visual observations can be used inside an engine to determine whether coolant is leaking across a sealed interface. However, the accumulation point may be a distance from the actual leak path, and a fairly high leakage rate is required before it is observable.
In order to provide a means for specifically determining the leakage path across gasket materials, it was decided to determine the feasibility of using radiotracers to detect and locate coolant leakage. An object was to measure precisely where the gasket interface was being breached. In addition, it was a more general object to develop the capability to measure small amounts of coolant contamination in oil.